Mohamed Morsi was sworn in as Egypt's first freely elected civilian president on Saturday and formally received a transfer of power and pledge of support from the military, which has ruled since last year.
"I swear by the Almighty God to sincerely preserve the republican order and to respect the constitution and law, and completely care for the people's interest," said the 60-year-old Morsi in a ceremony at the constitutional court.
The swearing-in, aired lived on national television, was delayed because of a dispute between Morsi, who did not want it broadcast, and judges, who insisted on it, one of the judges told the state's Al-Ahram newspaper.
Morsi had also wanted to take the oath before the Islamist-led parliament, but the military dissolved it earlier this month following a court order in what the Muslim Brotherhood described as a "soft coup."
In the handover at Cairo's Hike Step base, Field Marshal Hussein Tantawi pledged to support Morsi, who had been a senior Brotherhood figure until resigning from the movement after his election and with whom the army has had uneasy relations.
"We will stand with the new president, elected by the people," the head of the Supreme Council of the Armed Forces (SCAF) said in a speech after an honour guard parade and a helicopter fly-past.
He saluted Morsi and awarded him the highest military honour, "the shield of the armed forces."
Morsi thanked the military and pledged to support it.
"I accept the transfer of power," he said in his speech, at the same base where members of the once-banned Brotherhood had faced military trials under Mubarak.
Just after taking the oath of office, Morsi went to Cairo University to deliver a speech in which he pointedly mentioned the "elected parliament" several times and said the army should resume its normal role.
"The elected institutions will return to fulfilling their roles. And the great military will devote itself to the task of protecting the country," he said.
He then set out some of his international and domestic objectives, saying he would be a "servant of the people" in a "democratic, modern and constitutional state".
Internationally, he said Egypt respected would back the Palestinians and called for an end to the bloodshed in Syria.
"I announce from here that Egypt, its people and presidential institution stand with the Palestinian people until they regain all their rights," he said.
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He repeated that Egypt would respect its international treaties, in an allusion to its 1979 peace accord with Israel.
Morsi had spoken out forcefully in support of Palestinians during his campaign.
The Brotherhood is vehemently opposed to Syrian president Bashar al-Assad and supports the uprising against him.
But as president, Morsi is not expected to radically change his country's foreign policy, especially towards Israel, in which the military is expected to exercise its clout.
In a Friday speech before tens of thousands of supporters in Cairo's Tahrir Square, the epicentre of the revolt that ousted Mubarak, he said that he would insist on retaining all the presidency's powers.
"I renounce none of the prerogatives of president," he told his supporters, adding: "You are the source of power and legitimacy."
"There is no place for anyone or any institution ... above this will."
The SCAF assumed legislative powers after disbanding parliament and also formed a powerful national security council headed by the president but dominated by the generals.
The military also reserves the right to appoint a new constituent assembly should the one elected by parliament be disbanded by a court decision expected on September 1.
The Muslim Brotherhood insists that only parliament can appoint the assembly.
Media reports said Morsi was consulting a cross-section of Egyptian society before appointing a premier and a cabinet made up mostly of technocrats.
In a meeting with newspaper editors reported by most dailies on Friday, he pledged there would be "no Islamisation of state institutions" during his presidency.
Morsi became the Brotherhood's candidate to succeed Mubarak only after its first choice, Khairat El-Shater, was disqualified. He beat Ahmed Shafiq, Mubarak's last premier, with 51.73 percent of the vote.
Many had written him off as an uncharismatic substitute, saying he would be unable to muster widespread support.
But the powerful Brotherhood mobilised its formidable resources and supporters behind Morsi, who was appointed last year to head its political arm, the Freedom and Justice Party.